Bioparticles are biological materials shed from an organism. Compared to volatile compounds, bioparticles are generally present in greater quantities than volatile compounds, last longer in the environment, may be detected at lower levels, and provide a great breadth of physical or biological information. For example, many organisms including humans shed millions of skin flakes per minute, and each sneeze results in thousands of fine droplets of fluid. These settle slowly in the air and contain biological information potentially relevant to the identification of the individual. Bioparticles may be identified as being from a particular source which may then indicate the former or current presence of that source.
Identification of a biological source from evidence consisting of such bioparticles has relied upon forensic genetics based on polymorphism. However, forensic genetics based on polymorphism has utilized only a limited portion of DNA (deoxyribonucleic acid) polymorphism and has been based on low-effective techniques such as differential electromobility studies. Forensic DNA analysis, which includes analysis of restriction fragment length polymorphisms, PCR (polymerase chain reaction) analysis of variable number terminal repeats, and PCR analysis of short tandem repeats, requires the presence of high quality, intact DNA for a robust result. As shown, current methodology in forensic genetics is hindered by exacting requirements or low-effective techniques.
Even more, much of the matter released from an individual is made up of enucleated cells from the stratum corneum that have undergone apoptosis and hair shafts without any attached cellular material. Since these materials are nearly devoid of high-quality, intact DNA, DNA-based analysis of such bioparticles is of little use for identifying individuals. In addition, the scarce amount of DNA that may be present in these materials has typically undergone fragmentation in the process of apoptosis. Furthermore, even if a high-quality sample is present, it typically requires amplification by PCR. This, in turn, is problematic in that performing a PCR reaction is labor intensive, slow, and subject to false positive readings due to cross-contamination of other human DNA.
Other methods of identifying these bioparticles include the use of labeled reagents to selectively (i.e., specifically) target biological materials. The labeled reagents selectively bind to a biological target and emit a signal that indicates the presence of the material. The specific binding is typically achieved by use of any of a variety of biological probes, most notably proteins, including antibodies, antibody fragments, short peptides, and natural receptors for the component; carbohydrates; lipoproteins; and lipids known to be naturally specific for or created to be specific for a particular component of the material. Examples of molecules that send a signal include synthetic or naturally fluorescent molecules, enzymes that act upon a substrate to change it in an observable way, metal particles that allow labeled cells to be seen in a microscope or separated with a magnet, and radioactive isotopes. However, labeled reagents are typically costly, require special storage conditions, such as refrigeration, and may be slow in yielding meaningful data.
Methods that identify individuals based upon the release of shed materials without the need for DNA amplification or labeled reagents have relied upon the collection of volatile compounds, such as pheromones, cellular breakdown products, and the like. However, methods for the detection of volatile compounds suffer from several limitations, including the fact that volatile compounds are typically released from organisms in low concentrations, the volatile compounds of the organism can be confused with volatile compounds already present in the environment, and volatile compounds tend to disperse rapidly into the environment.
In view of the above, there is a need for a method to identify individuals based upon shed material and which avoids the difficulties and limitations of the methods currently practiced in the art.